青藏高原冻土区高寒草甸能量分配及蒸散发影响因子

高寒草甸的能量分配和蒸散发对青藏高原多年冻土区水循环至关重要。然而,能量分配、蒸散发及其驱动因素的季节变化(冻融循环)仍需要明确。因此,本研究在位于青藏高原风火山流域的高寒草甸进行了为期4年的能量通量(包括潜热和感热)观测,并估算了大气边界参数(包括表面导度,解耦系数和Priestley-Taylor系数)。研究结果表明,研究区日均潜热(27.45±23.89 W/m^(2))和显热(32.51±16.72W/m^(2))分别占可利用能量的31.71%和50.14%。在降雨期,更多可利用能量被分配到潜热;而在冻结期,67.54±28.44%的可利用能量分配给显热。显热在降雨期间是潜热的一半,而由于冻结期较低的土壤水分含量及植被盖度,显热在冻结期间是潜热的7倍。研究区年均蒸散发为347.34±8.39 mm/year,接近年均降水量。较低的日均解耦系数(0.45±0.23)和Priestley-Taylor系数(0.60±0.29)表明高寒草甸的蒸散发受水分供应限制。然而,在降雨期由于降水充足,蒸散发受到可利用能量的限制。在过渡期,蒸散发和降水之间存在较大差异,表明在该季节上游冰川和雪的融水通过侧向流动补给到土壤中。本研究的结果表明,在未来模拟多年冻土区水和能量通量时应考虑大气边界参数的季节变化。

Estimates of net primary productivity and actual evapotranspiration over the Tibetan Plateau from the Community Land Model version 4.5 with four atmospheric forcing datasets

The accuracy of the simulation of carbon and water processes largely relies on the selection of atmospheric forcing datasets when driving land surface models(LSM).Particularly in high-altitude regions,choosing appropriate atmospheric forcing datasets can effectively reduce uncertainties in the LSM simulations.Therefore,this study conducted four offline LSM simulations over the Tibetan Plateau(TP)using the Community Land Model version 4.5(CLM4.5)driven by four state-of-the-art atmospheric forcing datasets.The performances of CRUNCEP(CLM4.5 model default)and three other reanalysis-based atmospheric forcing datasets(i.e.ITPCAS,GSWP3 and WFDEI)in simulating the net primary productivity(NPP)and actual evapotranspiration(ET)were evaluated based on in situ and gridded reference datasets.Compared with in situ observations,simulated results exhibited determination coefficients(R2)ranging from 0.58 to 0.84 and 0.59 to 0.87 for observed NPP and ET,respectively,among which GSWP3 and ITPCAS showed superior performance.At the plateau level,CRUNCEP-based simulations displayed the largest bias compared with the reference NPP and ET.GSWP3-based simulations demonstrated the best performance when comprehensively considering both the magnitudes and change trends of TP-averaged NPP and ET.The simulated ET increase over the TP during 1982-2010 based on ITPCAS was significantly greater than in the other three simulations and reference ET,suggesting that ITPCAS may not be appropriate for studying long-term ET changes over the TP.These results suggest that GSWP3 is recommended for driving CLM4.5 in conducting long-term carbon and water processes simulations over the TP.This study contributes to enhancing the accuracy of LSM in water-carbon simulations over alpine regions.